Plaster compositions and products



States Patent P la-P assign to I Tl t d Products Corporsfiang' it ore; n w chi-i eration of Maryland N6 ti n-i st Apri s film July 30L1 '2, M! 39118.

a (Git-105 110) This a nslicaitoirisa c inution'i'n part of our copendinga glie tien seriar No: 2382782} filed July 26,

l'9 ilinowabandoiied'. K

This invention relates to ypsum plaster composition and products made there" q andparticularly' the inventionrelates to such c positions. and products thereof whereby increased" pr ect g ains't' fire} is attained.

In tee-pate t: 'Michel'e'f "N6.1 2;5'26,0 66 patented October- 17-; 1-950, thereis disclosed agypsum plaster compositionand product where y" an; unusual-1yhigh resistaance-to theheat of'th fir "attainedgfsuch plaster composition" and product at't jn'ing' this improved fire resistance characteristic ugh thecooperat-ingaction of-unexp'anded verniiculitmorporated in the plaster in a relatively small pereiitag'e' along with asmall percentage of" a" non-combiistible fiber such as asbestos. While the" manner in" which'= composition functions is disclosed" in dtet'zilin the aforesaid Croce patent, it may be=pointed out-thalt the primaiy 'reasonfor the improved resistance-to the action of the fire is that the expansion of the verni'iculite"wherfheatedby the fire is such 'as to substantially compensate for the inherent shrinkage of th'e gypsuiit'co'rii enter-the composition as such 'gyp sumcdmpbneiit is p essively calcined" and thermal insnlation asrtheveirnieuliteexpands; As pointed out in the' 'aforesaid Croce pa;ent 1ie inclusion 'of' the non-combus ti-hl'e 'fibe1 in e plaster composition is" for the purpose of preventin fla-king' or 'sp'allin'g of'the vermicul'ite as ueh Ver-micu 1a is expanded n tothe heat ofthe fire; 1t being fno't fthat' siich 'spal'ling; unless restrained t by the actionof place-'ina progressive in nter within-"a relatively v ens to destroy the wall iinein the event 'tha't 'no such The gypsum plaste composition-disclosed in the {aforesaid Croce'patentha's been commereially-used primarily forthe production of gypsum 'wallboa'rd' 'v'vherein'theusual paper liners on facing ni'embers a re' employed upon opposite sides of a coremade frofr'i the composition described in :the-aforesa'id' roce patcnt andas thus usedthe resultingf wallboard has met with-exceptional suceess attainingi exeremely high 'fire endurancefratings intests conducted at the*'-Uiiderwriters Laboratoriesat Chicago, Illinois, such testsbeing conducted 'uponceilings as well as 1 load beaning partitions' according-"to I standard "methods of fire testsnf building construction"and rnaterials.

Despite such'su'ocess of -the' ypsum plaster composition' describe'd -in the' aforesaidlflroce"patent, it is the primary object of the present inventio'n tc ienable-further increases in -fire'resistance to be attained -by plaster composition materials and products 0f the general character shownzinthe Croceflpatent; and to attain such improve ments ina way that not only:facilitatesmanufacture but also reduces the manufacturing cost;

One of the primary reasonsrwhy gypsum plaster walls afford an effective means forretarding'the'progress; of the fire isthat; he set: =8P$1 ntpplastercontains somewhat over 20% of chemically combined water which is many b'ouyin gnw; would take I increase in the gypsum plaster content of s uch'com water over and above the amount of waterfihat would 2 times referred to as the combined water in the set plaster, and when such a plaster wall is attacked by actual wall temperature cannot become exce I, 7 until substantially all of the. combined water in th V has been driven on by whatoun ts t calcination of the plaster. W hisin ent, of course, that where a gyps m plas r compos onfl i s employed that includes foreign o" additive materials 0 er than plaster, the foreign m a ls v re a d stance at a material, saerilice insofar as the bi'n'e'd water content of the' fina l wall be con med, and -it is a further and impor t'ant object of the I invention to nab e a: ste te ei tiq ffi K4 3i plaster composition suchas' that of the aforesa d qroce patent to be materially increased, and ob lets related, to the foregoing are to enable required fiber content in plaster compositions, f the ,flfQre said cha cter Ito be materially reduced so as to therebypermi tions; to. enable the noncombustible-fiber content inlsu c h gypsum plaster compositions to be afio r ded bynon-cornlb'us tible fibers that may be readily easily and thoroughly dispersedinsuch compositions. I f

In the commercial production of plaster wall};'oai'rl in accordance with the disclosure of the aforesaid C e patent, it has been determined that the most aiivanta one results are obtained when the noncombustible fiber afforded by 2% of asbestos'fibe'r, it having, heenifo'und that the use of blown glass fiber or glass-wool asdesc 'b'ed inv such patent introduced manufacturing difiiculties in some instances because of the tendency of such glass Wool to form into lumps or balls'in the course of: the mixing of the gypsum slurry. In SElQli use of asbestbs 'as the non-combustible fiber in wallboard .ma'de under the aforesaid Croce patent it is found that the asbestos absorbs excessive amounts of water during the m operation so that in order-to obtain a workable epns is tency' in the slurry it is necessary to'add'con s iderable be required if the asbestos were not employed h additional mixing water must of course be e the course of the drying operation, and'this s b p I able. It is, therefore, another important obje'c ti of the present invention to enablethe fiber content tobe'afforded in vermiculite-plaster compositions insuch;

a ,Way as tominimize the amount of mixing water that must be employed. More specifically it is an lobjec t of the present invention to enable glass fibers to be readily jand' easily lo in gypsum, P as s mi ie s' tbe e ie el type disclosed in the aforesaid Croce patent, and: to'util'ize such glass fibers in such a ay that these glass. fibers attain, what amounts to a'co'mplete and uniform dispersion throughout the mass of-acastimade from such composition. I

The composition and product of the present invention; as pointed out hereinabove, constitute an improvement on the composition and product disclosed in the aforesaid Croce Patent No. 2,526,066,;and- .is-a broad sense the composition of the present invention'comprises cal cined gypsum plaster, comminuted unexfoliated' vermiculite so proportioned by itssize, quality and: relative quantity as to afford an inherent expansion which will" sub stantially equal the shrinkage of the'set gypsum: under the action of a fire, and a bodyingfiber conte'nt'aiforded inmost instances by an extremely minute proportion of drawn textile glass fibers cut intoshortlengths'and capable of substantially complete dispersion in the composition as such compoistion is mixed into a slurry form. I -n respect'to the relative quantity, the quality and the fineness. or grading of the. vermiculitel component of the com position, the disclosure of the aforesaid Croce patent is directly applicable to the present invention, and is by reference incorporated herein in all its detail.

Considering first the variations of size or grading, quality and relative quantity of the vermiculite group, that is used as the heat-expansible component of the composition, it is known that such minerals from different sources expand in different amounts, and that the eifectivc expansion of such minerals, regardless of source, varies with the degree of comminution of such mineral. Since the heat-expansible mineral is incorporated in the plaster composition for the purpose of counteracting the shrinkage of the gypsum plaster component under the action of fire, but without objectionably exceeding such shrinkage, it follows, as taught by the aforesaid Croce patent, that the proportion of the vermiculite component must vary in accordance with the size and the quality or source of the mineral that is used. In the absence of any known formula for expressing the relationship between the size, quality and relative quantity factors as applied to the vermiculite component, this relationship has been defined functionally in the aforesaid Croce patent by reference to the amount of the total expansion attained by highgrade vermiculite of a particular size or grading and within specified limits of percentage.

Thus it was found as explained in the aforesaid Croce patent, the vermiculite from the mines at Libby, Montana, had a greater expansion than vermiculite from any other known source, and the vermiculite from this particular source was, therefore, designated as being highgrade; and in the Croce patent it was taught that expansion within the required limits could be attained through the use of such high-grade vermiculite in a percentage of from 2 /2% to and in a minus 28 mesh commercial grading. The phrase Minus 28 mesh com mercial grading is to be taken as meaning material ground by usual grinding processes to a degree such that all of the material will pass through a usual 28 mesh testing sieve. This teaching was then utilized in the claims of the aforesaid Croce patent to define and relate the various factors pertaining to the vermiculite component as follows:

the degree of comminution of the mineral of the vermiculite group and the grade and amount of such mineral used being such that when the cast made from such mixture is heated to a high temperature the expansible mineral in the cast shall have about the same total amount of expansion as would 3 /2% to 7 /2% of high-grade vermiculite of minus 28 mesh commercial grading,

At the outset it should be noted that suggestions have heretofore been made concerning the use of glass fibers, glass wool or mineral wool in hydraulic cement mixtures or gypsum plaster mixtures for reinforcing or strengthening purposes, or as in the aforesaid Croce patent, for the purpose of retaining the expanding vermiculite in place in a cast, but such prior suggestions along this line have been found to be unworkable in a commercial sense, particularly insofar as to plaster molds, casts, walls and wallboard were concerned. This impracticability of such prior suggestions has resulted from the tendency of the glass fibers or mineral wool to form agglomerate masses or balls in the mixed plaster or slurry, as contrasted with the desired dispersal of the fibers uniformly throughout the mixture. In contrast to such objectionable action of glass wool or mineral wool as suggested in the prior art, the present invention attains substantially complete and uniform dispersal of glass fibers in gypsum plaster slurry so as to thereby attain a radical improvement in the desirable physical characteristics of the resulting casts, and this is attained at a relatively low cost and in such a way as to simplify and facilitate the manufacturing and other operations involved in the mixing and forming of the slurry.

Glass fibers may be classified generally in two main categories or groups as blown glass fibers or as drawn textile glass fibers, and while these classifications are based upon the method of production of the fibers, there also are many definite and important distinctions between such groups as to physical characteristics and properties of the fibers as well as in the relationship of the individual fibers to each other. Thus, blown glass fibers are formed by steam blowing of a molten glass stream to attenuate the stream into small diameter fibers, and such fibers take a form known generally as glass wool or mineral wool in that the fibers are not straight and are interlaced in a random relation with each other. The fiber length may vary considerably in such glass wool, and separation of individual fibers from the mass is quite diflicult because of the curled and interlaced or matted relationship of the fibers in the mass. Such separation of individual fibers from the mass is also rendered difficult by reason of the relatively physical strength characteristics of the blown fibers which bend quite easily and tend either to retain their bent form or to break at the bend.

The drawn textile glass fibers are on the other hand produced as continuous filaments, each of which is discharged in a molten state through an orifice and is attenuated by winding on a high speed winding drum. In the production, winding and handling of drawn glass fibers or filaments it is essential that a great many such extremely fine filaments be grouped into strands each containing from one hundred to several hundred individual filaments so that the forces that are necessarily involved in the high speed handling will not cause breakage of the filaments. Because of such grouping, the abrasive character of the glass makes it necessary as a practical matter to apply a protective coating to such filaments to prevent abrading action between the several grouped filaments of each strand. Such protective coating material is usually termed the bonding material although the actual bonding action where very small quantities of binder are used or in the case of some of the commonly used coating materials such as a starch coating is relatively slight, so that the fibers or filaments may in such instances be said to be loosely bonded or loosely associated. In other instances, the coating material may be of such a character or may be used in such quantities as to hold the filaments of the strand quite permanently together and some thermoplastic resins when used as the bonding material act to produce such a strong bond in the strand.

Under the present invention, resort is had to the use of the more costly drawn textile glass fibers that are loosely bonded or loosely associated and by attaining complete dispersion of such fibers in the mixture in the manner described hereinafter, the full strengthening and bodying effect of each of the individual fibers is realized with the net effect that the quantity or proportion of the drawn glass fibers is minimized and the use of the costly fiber is rendered practical in an economic sense.

The drawn glass fiber component of the plaster composition is aiforded by a small percentage of drawn textile glass strands cut into short lengths and incorporated in the gypsum plaster, and such glass fibers are of such a character that they will separate and attain an almost complete or individual dispersion of the individual filaments as a slurry is formed from the plaster composition. Such drawn glass fibers, of course, may be of different diameters but are in any event extremely small or fine. Thus, fibers having a diameter of about 0.00024 inch to about 0.00038 inch which are commercially available, has been found to be highly effective as will be described in detail hereinafter.

The glass fiber material utilized under the present invention is one which is loosely bonded or associated into strands as by a bonding material that is water softenable or water soluble in character, and the strands are cut into short lengths, within the range of A inch to one inch so as to afford short sections or bundles of fibers, each bundle being formed by a cut length of a strand, and it has been found that a length of about one-half inehrisi new? satisfactory-, Under the: present: invention therbinden: iSF-Bifibl'lllfidf. by: a water: softenable or a water aelubleimatelial such;asiarstanchrmaterial orwater softenahles-resinse. andiic is; found? thatr-withv such a binder the he balance of-i hl6= Q m1l0S OIt5b l$ ffordedy' a cined= gypsum plaste s; andth:1ell;gfllrf'; fibersrmay be vari d e ween about /l""i l T and: one; inch; audit: is t nders ood of o rse, hat the present invention individuals-filaments:whichimake@upeach; bundle or-short 5 contemplates the use} of? smalli added? quantitiesrofi reseetion of en-suchter'rd;- to remain; together in their bundle tarders, accelerators, StfllfllflSQf core--adhesives= and the im. that-course v ofi-ai short dryrmixing operation withl the like in: accordance withusual practi'c gas-:wellfias; the other componentm of: the: plaster? composition, although additio'mof w ight reducingvfoam and-core; adhesivewhen tberevisrat substantiali separationi of; the filaments; from the presentinyentiomisremployedrintthe'manufactureof theirbundlesi-asi-such;dry-mixing progresses. gypsum wallboard;orlikeiproducts l thisfshontr-bllndleiliki form; the: strength and; re: Under; the present. invention; has; boom-discovered silienoeroft-the bundles zand of: theifibers is sufliciently that the-bodyingt-fiher-contentinfire retardantrcomposir highrttrrpreventr reakingzofithmstrand or, the individual tionseoft the, character discussed above-may,- be afforded filiersiizon filamen by, the; forces: that may be applied by, from -three-hundredths of one; pereent (-0 03 to thereto-1m ar -niixinggoperations Moreover thestrength threeetenths-of-onepercent-;(Q,3% f drawn- -textile,glass springin'esssoftherindividuahfibersaand the bundles fiber cut into short-lengthsvas abovesdeseribed Thus, asrdmparodrtoitlierforces: that may: be; appliedv thereto compositions including ;a control, sarnp madeaceording imaidfat omwet: mixingmperatiomwith the plaster;-is,:suifito: the Croce patent; havesbeenf; nadeaDdFtCStQQpiDFaQT cient to prevent the formation of swirlsylballsior; agglomcordance thefollowing -table Ingredients-Percent Tests in }6 Inch Slabs izm f t. V bundles High Grade 1 Chang 1 7 1 spamngfi Formula/N, Peera ease Page eate arge s described vermiculite 1,300'E 1 YB E 3 11 96.4 None; /z 5, Slight. 3% 96:47 I Do;-

8- LQQ l IaD Q-i 7.0 T 92.9 None: 7. 0 92-95 Considerable m: 9197 o.

s 0.02 7.0 92, 93 (1-1, Asbestos 2v0.' 3% 9415, None.

GIBI-QlmBSSQSJ-H Hence; ali-mixingsoperationithatis applied tofiaecomposition rwhich'vinclndes relatively. short bundles of loosely bonded-drawnglass-fillers; as aforesaid is effectine; primarily; tolproduces uniformity of; distribution of thenbnndlessand individual fi elisqthliollghtllll the mass of material. As hereinabove pointed out, the dry mixing operation doesin fact tcausewseparationwofrindividual fibers or small-t groups} ofefiberl's frpmt-the-- bundles, but :suchaction islrelatiyel-y, slowrsotlong; asrthe water: soluble: or water softenable binder? .i.-not-fsubicted to the action of water; Suelr dryfl'IfiXiBg'mBy, of course; be carried on until,- the flbersrhave been completely; separated from their bundles and oompletelynldispersed -in1-th,e dry. but this is usually;yconsidered;- unneeessary inrviewof tthe ease of 'disperjsiom-imthew-final wet mix. The preliminary distributions ofithe: bundlesaand .individual;glassg fibers in a short-dry mixingoperation serves;-however, to simplify smalhbatehmsageof. the -mixturer= as-well 1 as-to simplify thes wet mixing goperationwand-when-the water is fed into the plaster composition 'lnrthfiwwet mixer, the action of the water iimrnediatelyydissolyeson softens the binder to such an iextentrthaterelatively shortwet mixing operation periormed forrexample; ,in a continuous-mixer causes pretilicallyv cornplete sl paration of. the individual drawn glassdibers. from itheinrbundle form ;so that such individual glas fiberearetalrnost c0mPletely-dispersed in a uniform manner; throughout .thei-bodyof the slurry. Then inthe mold-ingotcastingoperationthe individual glass filaments are llfiformlwlocated throughout themass with what might zberterrnech a;-rand0m dispersion as to relative directiomavithimthe cashand it is by reason of this thorough ditpersion=andthe --randomrelationship, of the direction oft thevin,iilidnaltfibersr thatlthe-fibers form a skeletal matelike retainingnstr-ucturewhich elfectually prevents spelling ofthe-expanding,wermiculite. in caseof a fire.

:Tlieipercentage -.by% I weight: of loosely bonded drawn fibexiusedaunder thegprelsent invention isfrom 0.03% toi ll-flilailvdwithrfromefi ar atom/% nof'ihigh grade; vermicu: lite in a minus 28 mesh commercial grading and with Gonsideration of the foregoing-table'with partictilar reference. to the'included test-data showsthan the percentageof draw-n glass fibermusty-beincreased; withtthe increase in the percentage of -vermiculite, and in further 'showswthatl within; the operablerange 95111.67 vermiculite com onenh-the critical lower limitrofs the drawn glass fiber component is substantially .03 percent; It isimportant to note that eveniat thes maximum vermiculite content of 7 percent, theuset ofbutb. 1 percent o fdrawn gass fiber controlsthe; spallingiof thewvermiculite, while with a- 10W vermiculite content-,ofi 3 gpe rc ent, such controlis. attained by .03 percent Of dI'aW-Ilglass fiber.

Another important: advantage attained is that of re.- ducing the amount of' mixinggtwater required, it having been determined that withany, of:- the, formulae from lto. 8, theamount-olf mixing ew aterv-isj substantially 15% lessthan with formula Gael which.:containsz-2%.- oi as; bestos. This, of course greatlyreduces: thedryingztime .ofcastsimade from. the composition.

The plaster compositionof the present invention may of course have the: desiredretardants, accelerators and the like added theretolaccordin usual-practice, and the same isv trueein respect to :weight reducing'materials such as foam: which is particularly desirable in the making of plaster wallboard. The composition may of-course be usedtin: producing lath and; plaster-walls in the cone ventional way where aplaster surfacingmade from the above, described composition is shown. as applied to, lath of the usual kind and construction;

Plaster wallboard may also be made having-paper-covers orrlinersenclosinga core made, fromthe composition of the present invention,- andin-making Such w ll oard it is -tobev noted that thousual smallipierecentagfi-of-core adhesive may --b e incorporated in 5 the-slurry used in :forming the core, in accordance with usual practice: in the wallboard art inrorder I to. assure firm bo'nd of the liners withthecore The slurry'used'in'makingatheplaster walb board: may also-contain the: usual' amount: {of weightreducing foam.

The unusual efiectiveness of extremely small percentages of drawn glass fiber in attaining high fire endurance rating in plaster wallboard was shown by comparison of similar boards made in inch thickness and subjected to similar ceiling tests for fire endurance rating at the Underwriters Laboratories, Inc. in Chicago. Such /8 inch wallboards each contained Il /2% of high-grade unexpanded vermiculite of minus 28 commercial grading, together with the usual proportion of core adhesive and weight-reducing foam, while the first such board contained 2% of SR asbestos and the second such board contained 0.2% of drawn textile glass fiber cut to V2 inch lengths and originally bonded by a water softenable binder.

These boards were subjected to similar fire rating tests for ceiling use, and it was found that while the board containing asbestos would not attain a rating of one hour fire resistance, the second board which contained drawn textile glass fiber as aforesaid attained a rating of slightly over one hour. In these tests it was noted that, in the ceiling made from such second board, the board remained intact on the ceiling for about ten minutes longer than the first board.

The fact that the plasterboard made under the present invention remained intact and in place for an additional ten minute period is of course an important factor, and a study of the board thus tested has shown that despite the great heat of the fire in the test, the drawn textile glass fibers in substantially the upper or back half of the board were still intact, while such fibers in the lower or front side of the board were not perceptible to any marked extent and had been melted as the fire progressed. The glass fiber in the lower or front half of the board had, however, retained its strength and form during the earlier stages of the fire while the expansion of the vermiculite was taking place, thus to hold such expanding vermiculite and the adjacent plaster against spalling, and thus an insulating zone, including the expanded vermiculite was built u in the lower or front half of the board which served to protect the fiber in the upper or rear half of the board. The glass fiber in the upper or rear half of the board thus retained its full reinforcing and strengthening function so as to maintain the board intact for an increased period of time. The board thus serves as a fire curtain for an increased period, and the expanded vermiculite in the lower or front zone of the board serves as an improved heat insulating barrier to retard temperature rise on the remote or back side of the board or partition.

In the board that was thus tested, the amount of drawn textile glass fiber was quite small, that is 0.2 percent, and this amount was sufiicient to hold 3% percent of minus 28 mesh high grade vermiculite against spalling. In view, however, of the continued reinforcing action of each glass fiber that occurs as hereinabove described an even greater resistance to the action of a fire may be attained, where this is desired, by increasing the drawn textile glass fiber content of the mixture over and above the amount required to prevent spalling. Such increase may be carried up to about one percent of drawn textile glass fiber without adversely affecting the mixing and handling operations. Such an increase in the fiber content acts to increase the strength of a plasterboard or the like, and when the exposed face of the board is subjected to a fire, the rear portions of the board, in which the fiber is protected and remains intact as described hereinabove, possess in' creased strength so as to cause the board to remain intact for an even longer time.

Thus it will be apparent that the present invention enables high fire endurance in plaster casts to be attained in such a way that manufacture of cast plaster products is materially simplified, and this result is attained at a cost which is materially less than could heretofore be attained.

We claim:

1. A composition convertible by water addition into a settable plastic mass, said composition consisting essentially of calcined gypsum plaster, comminuted unexpanded vermiculite and sections of textile glass fiber strands, the length of said sections of textile glass fiber being between one quarter inch and one inch and comprising not substanti ally less than .02% and not substantially more than 1.0% by weight of the total weight of said unexpanded vermiculite, said textile glass strands and said calcined gypsum plaster, each of said sections of textile glass fiber strands being composed of a plurality of individual textile glass filaments bonded together in substantially parallel relationship in said strand by a water softenable binder, said binder being sufiiciently weak to enable substantial separation of said strands into individual filaments throughout said plaster as an incident to the agitation of said composition with water, the particular degree of comminution and the grade and amount of said unexpanded vermiculite being such that when heated to the calcining temperature of said gypsum plaster said vermiculite shall have substantially the same total amount of expansion as would 386% to 7 /z% of high grade vermiculite of minus 28 mesh commercial grade.

2. A composition convertible by water addition into a settable plastic mass, said composition consisting essentially of calcined gypsum plaster, high grade comminuted unexpanded vermiculite of about minus 28 mesh commercial grading and sections of textile glass fiber strands, the length of said sections of textile glass fiber being between one quarter inch and one inch and comprising not substantially less than .02% and not substantially more than 1.0% by Weight of the total weight of said unexpanded vermiculite, said textile glass fiber strands and said calcined gypsum plaster, each of said sections of textile glass fiber strands being composed of a plurality of individual textile glass filaments bonded together in substantially parallel relationship in said strand by a water softenable binder, said binder being sufiiciently weak to enable substantial separation of said strands into individual filaments throughout said plaster as an incident to the agitation of said composition with water, said high grade comminuted unexpanded vermiculite comprising not substantially less than 3 /2% and not substantially more than 736% by weight of the total weight of said unexpanded vermiculite, said textile glass fiber strands and said calcined gypsum plaster.

3. A plaster cast consisting essentially of set gypsum plaster, said set gypsum plaster containing dispersed therein comminuted unexpanded vermiculite and textile glass filaments, the particular degree of comminution and the grade and amount of said vermiculite being such that when the cast made from such mixture is heated to a high temperature the vermiculite in the cast shall have about the same total amount of expansion as would 3 /2% to 7 /2% of high grade vermiculite of minus 28 mesh commercial grade, said textile glass filaments having a length not substantially less than one quarter inch and not substantially greater than one inch and being distributed substantially uniformly as individual filaments throughout said set gypsum plaster and comprising not substantially less than .02% and not substantially more than 1.0% by weight of the total weight of the unexpanded vermiculite, the textile glass filaments and the gypsum plaster of the raw batch.

4. A plaster cast consisting essentially of set gypsum plaster, said set gypsum plaster containing dispersed therein high grade comminuted unexpanded vermiculite of about minus 28 mesh commercial grading and textile glass filaments, said high grade comminuted unex anded vermiculite comprising not substantially less than 3 /2% and not substantially more than 795% by weight of the total weight of the unexpanded vermiculite, the textile glass filaments and the gypsum plaster of the raw batch, said textile glass filaments having a length not substantially less than one quarter inch and not substantially greater than one inch and being distributed substantially uniformly as individual filaments throughout said set gypsum plaster and comprising not substantially less than .02% and not substantially more than 1.0% by weight of the total weight of the unexpanded vermiculite, the textile glass filaments and the gypsum plaster of the raw batch.

5. In a plaster board, a body member having a paper cover on at least one face thereof, said body member consisting essentially of set gypsum plaster, said set gypsum plaster containing dispersed therein comminuted unexpanded vermiculite and textile glass filaments, the particular degree of comminution and the grade and amount of said vermiculite being such that when the cast made from such mixture is heated to a high temperature the vermiculite in the cast shall have about the same total amount of expansion as would El /2% to 7V2% of high grade vermiculite of minus 28 mesh commercial grade, said textile glass filaments having a length not substantially less than one quarter inch and not substantially greater than one inch and being distributed substantially uniformly as individual filaments throughout said set gypsum plaster and comprising not substantially less than .02% and not substantially more than 1.0% by weight of the total weight of the unexpanded vermiculite, the textile glass filaments and the gypsum plaster of the raw batch.

6. In a plaster board, a body member having a paper cover on at least one face thereof, said body member consisting essentially of set gypsum plaster, said set gypsum plaster containing dispersed therein high grade comminuted unexpanded vermiculite of about minus 28 mesh commercial grading and textile glass filaments, said high grade comminuted unexpanded vermiculite comprising not substantially less than 3 /2% and not substantially more than 7 /2% by weight of the total weight of the unexpanded vermiculite, the textile glass filaments and the gypsum plaster of the raw batch, said textile glass filaments having a length not substantially less than one quarter inch and not substantially greater than one inch and being distributed substantially uniformly as individual filaments throughout said set gypsum plaster and comprising not substantially less than .02% and not substantially more than 1.0% by' weight of the total Weight of the unexpanded vermiculite, the textile glass filaments and the gypsum plaster of the raw batch.

References Cited in the file of this patent UNITED STATES PATENTS 2,425,883 Jackson Aug. 19, 1947 2,526,066 Croce Oct. 17, 1950 FOREIGN PATENTS 587,556 Great Britain Apr. 29, 1947 830,030 France May 2, 1938 

1. A COMPOSITION CONVERTIBLE BY WATER ADDITION INTO A SETTABLE PLASTIC MASS, SAID COMPOSITION CONSISTING ESSENTIALLY OF CALCINED GYPSUM PLASTER, COMMINUTED UNEXPANDED VERMICULITE AND SECTIONS OF TEXTILE GLASS FIBER STRANDS, THE LENGTH OF SAID SECTIONS OF TEXTILE FIBER BEING BETWEEN ONE QUARTER INCH AND ONE INCH AND COMPRISING NOT SUBSTANTIALLY LESS THAN .02% AND NOT SUBSTANTIALLY MORE THAN 1.0% BY WEIGHT OF THE TOTAL WEIGHT OF SAID UNEXPECTED VERMICULITE, SAID TEXTILE GLASS STRANDS AND SAID CALCINED GYPSUMPLASTER, EACH OF SAID SECTIONS OF TEXTILE GLASS FIBER STRANDS BEING COMPOSED OF A PLURALITY OF INDIVIDUAL TEXTILE GLASS FILAMENTS BONDED TOGETHER IN SUBSTANTIALLY PARALLEL RELATIONSHIP IN SAID STRAND BY A WATER SOFTENABLE BINDER, SAID BINDER BEING SUFFICIENTLY WEAK TO ENABLE SUBSTANTIAL SEPARATION OF SAID STRANDS INTO INDIVIDUAL FILAMENTS THROUGHOUT SAID PLASTER AS AN INCIDENT TO THE AGITATION OF SAID COMPOSITION WITH WATER, THE PARTICULAR DEGREE OF COMMINUTION AND THE GRADE AND AMOUNT OF SAID UNEXPANDED VERMICULITE BEING SUCH THAT WHEN HEATED TO THE CALCINING TEMPERATURE OF SAID GYPSUM PLASTER SAID VERMICULITE SHALL HAVE SUBSTANTIALLY THE SAME TOTAL AMOUNT OF EXPANSION AS WOULD 3 1/2% TO 7 1/2% OF HIGH GRADE VERMICULITE OF MINUS 28 MESH COMMERCIAL GRADE. 